Couplers having muff couplings of the kind generally mentioned above are used above all for the coupling of rail-mounted vehicles of different types, e.g., carriages or wagons and/or locomotives in train units. More precisely, each end of the individual carriage is connected with a coupler, which can be coupled together with a compatible coupler in the nearby carriage in the train unit. In the modern railway technology, only automatic or semi-permanent central couplers are in all essentials used in which the requisite damping function between the carriages is integrated, i.e., the carriages lack separate dead blocks. In one respect, the couplers may be divided into two main types, viz. a simpler type that utilizes hooks as coupling elements, and a more sophisticated type that makes use of more complicated latch mechanisms.
Common to all types of modern couplers is that they are manufactured by a specially adapted modular structure so far that the couplers—in order to provide for different purchasers' individual needs and wishes—are put together from a variety of different components of standard type as well as special designs, this providing finished couplers having highly varying properties in respect of, for instance, inherent strength, length, force transfer capacity (tension and compression, respectively), shock absorbing capacity, crash absorption capacity, price, service friendliness, possibilities to repair, etc. The need for specially adapted manufacture is particularly marked in the light of the fact that only a few actors serve the entire world market for couplers and that the railway traffic in the different countries of the world is controlled by national rules and regulations of shifting character, e.g., in respect of security, speed, travel comfort, timetable reliability, topography of landscape, etc. Therefore, the components that are found in the couplers vary in number and nature. Thus, in central couplers, there may be included, according to the individual specification of requirements from the purchaser, in addition to a head, for instance, shock absorbers or dead blocks, length-determining extension or spacing collars, crash-absorbing deformation tubes, leading anchors, pivot brackets and the like.